Maeve Duffy

Calculation of self and mutual impedances in planar magnetic structures

The high frequency operation of magnetic components, in applications such as filters, makes them ideal candidates for thick film technology along with resistors and capacitors. This in turn leads to distinct advantages over labor intensive wire wound components: improved reliability, repeatability, accuracy and consequential cost reductions. This paper establishes a new set of formulas for the self and mutual impedances of planar coils on ferromagnetic substrates. A planar coil in air is a special case of the generalized formulas. The formulas are derived directly from Maxwells equations and therefore serve as a useful yardstick for simpler approximations. The formulas take full account of the current density distribution in the coil cross-section and the eddy current losses in the substrate. Experimental and calculated impedances up to 100 MHz are presented for a four layer device with three turns per layer which is 150 /spl mu/m thick and 40 mm/sup 2/ in area. >

Calculation of self- and mutual impedances in planar sandwich inductors

High-frequency planar magnetic components, employing thin film and thick film technology, have become important components in applications, such as filters and switching converters, due to their ease of manufacture and reliability. In a previous paper, the authors established a frequency dependent impedance formula for planar coils on a magnetic substrate that is infinitely thick. In this paper, two new impedance models are described: the first is for planar coils on a magnetic substrate of finite thickness, and the second represents a planar coil sandwiched between two substrates. The models include the electrical conductivity of the magnetic material so that the effects of eddy currents, particularly at high frequencies, are taken into account. The eddy currents reduce the inductance and increase the losses associated with the device. The new impedance formulas are derived from Maxwells equations. Simulations were carried out on a typical device, using finite element analysis, and the results validate the new formulas. This paper establishes the frequency limitations of lossy magnetic substrates.

PCB integrated inductors for low power DC/DC converter

This paper discusses the use of printed circuit board (PCB) integrated inductors for low power DC/DC buck converters. Coreless, magnetic plates and closed core structures are compared in terms of achievable inductance, power handling and efficiency in a footprint of 10 /spl times/ 10 mm/sup 2/. The magnetic layers consist of electroplated NiFe, so that the process is fully compatible with standard PCB process. Analytic and finite element method (FEM) methods are applied to predict inductor performance for typical current waveforms encountered in a buck converter. Conventional magnetic design procedures are applied to define optimum winding and core structures for typical inductor specifications. A 4.7 /spl mu/H PCB integrated inductor with dc current handling of up to 500 mA is presented. This inductor is employed in a 1.5 W buck converter using a commercial control integrated circuit (IC). The footprint of the entire converter measures 10 /spl times/ 10 mm/sup 2/ and is built on top of the integrated inductor to demonstrate the concept of integrated passives in power electronic circuits to achieve ultra flat and compact converter solutions.

A review of planar magnetic techniques and technologies

This paper presents an extensive survey of techniques and technologies used to implement planar magnetic structures in modern DC to DC converters. The survey emphasises the practical applications of these devices. The trends are analyzed in the context of the marketplace and some predictions of future direction are attempted.

Electromagnetic generators for power harvesting

The design of electromagnetic generators that can be integrated within shoe soles is described. In this way, parasitic energy expended by a person when walking can be tapped and used to power portable electronic equipment. Designs are based on discrete permanent magnets and copper wire coils, and it is intended to improve performance by applying micro-fabrication technologies. Detailed descriptions of design and measurements of initial prototype structures are presented, with which RMS voltage levels of over 500 mV have been achieved. Predicted power levels are comparable to those achieved with integrated piezoelectric generators. The design of a second generator structure is introduced. A comparison of the two types of electromagnetic generator structures is presented.

Modelling and analysis of a magnetic microactuator

This paper describes the operation of a magnetic microactuator. A prototype device consisting of a Nd-Fe-B permanent magnet, a silicon membrane and an electroplated copper coil is used to verify models and to predict the deflection of the magnetic microactuator. The analysis of this device involves the investigation of its electromagnetic and mechanical behaviour using analytical methods and finite . element analysis FEA . A design procedure for a magnetic microactuator is also outlined. The prototype device was characterised and the measured results compared to the theoretical data. Results show that the deflection of the device may be predicted to an accuracy of 20%. q 2000 Elsevier Science S.A. All rights reserved. .

Impedance formulas for planar magnetic structures with spiral windings

It is well established that magnetic components may be reduced in size by operating at high frequency. Miniaturization of magnetic components is ideally suited to microelectronics technologies such as thick films, which lend them to planar geometries. This paper describes new analytical models, which predict inductance- and frequency-dependent eddy-current losses in magnetic substrates. Prototype devices were fabricated by a thick-film process with four layers of conductors on a single ferrite substrate and in a sandwich configuration, consisting of conductors between ferrite slabs. The prototype devices were tested in the frequency range 10 kHz-100 MHz. The measurements confirm the validity of the analytical models. Simulation with finite-element analysis was employed to identify different sources of losses: eddy current losses in ferrite substrates; proximity effect losses in conductors; and dielectric losses.

Packaging and integration technologies for future high-frequency power supplies

This paper reviews data from the International Technology Roadmap for Semiconductors to establish where dc-dc converters are headed in the first decade of the new millennium. It focuses on the high performance computing (high current, fast response, high power density) and portable/handheld (low profile) sectors. Magnetics and power device packaging technologies needed to allow power supplies to move to operating frequencies in the 1-10 MHz region are discussed. It introduces the concept of magnetic components fully embedded (windings and core) in PCB and silicon offering low profile and low losses at high frequency. It also reviews developments in wirebond-free power packaging such as flip-chip assembly that offer low profile, reduced parasitics and increased thermal performance. Finally, consideration is given to the changes in the power electronics industry that may need to be addressed to enable these new technologies to play a strategic role.

Design study for ultra-flat, PCB integrated inductors for low power conversion applications

In this paper the effectiveness of integrated cores is investigated as a function of various core parameters. This is a step towards optimised magnetic structures for this novel type of component.

New method for integration of resonant inductor and transformer-design, realisation, measurements

For the miniaturisation of resonant converters the resonant inductor has been integrated into the transformer by using the leakage inductance as the inductor. A new method of adjusting the leakage inductance for planar transformers with integrated windings by using an additional layer of low permeable magnetic material is introduced. The leakage inductance of planar transformers with integrated windings can be adjusted very precisely and reproducibly.